The present invention relates to implantable devices, and more particularly, to a fully implantable device or system for stimulating or sensing living tissue wherein the implantable device has a rechargeable battery or other replenishable power source. One aspect of the invention relates to an implantable device configured to minimize heat generation due to eddy currents during battery charging and other magnetic powering. Another aspect of the invention relates to partitioning the circuit functions within the implantable system to allow upgrading the circuit functions and/or to permit existing partially implantable systems (having both implanted and external, or non-implanted, components) to be converted to fully implantable systems.
Presently available implantable stimulation devices, such as a cochlear implant device or a neural stimulator, typically have an implanted unit, an external ac coil, and an external belt-mounted control unit and power source. The external control unit and power source includes a suitable control processor and other circuitry that generates and sends the appropriate command and power signals to the implanted unit to enable it to carry out its intended function. The eternal control unit and power source is powered by a battery that supplies electrical power through the ac coil to the implanted unit via inductive coupling for providing power for any necessary signal processing and control circuitry and for electrically stimulating select nerves or muscles. Efficient power transmission through a patient's skin from the external unit to the implanted unit via inductive coupling requires constant close alignment between the two units.
Rechargeable implantable sensing and/or stimulation devices (e.g., heart pacemakers) are relatively bulky devices (e.g., 3 inches.times.2 inches.times.0.5 inches) and are quite heavy. Further, these rechargeable implantable devices require a substantial amount of charging time each week.
Accordingly, there exists a need for a small lightweight implantable device that does not require constant external power and that includes a long-lasting internal battery that may be recharged within a relatively short time period.
Further, there exists a need, should the battery within such a small, lightweight implantable device malfunction, or should the user desire to not use the internal battery for certain time periods, to still be able to provide power to the device, e.g., from an external power source, so that the device can continue to operate and provide its intended function, e.g., sensing and/or stimulating, to the patient, without having to implant a new device in the patient. Further, there exists a need for a fast, simple method for the battery module to be replaced during surgery, should replacement be necessary or desired.
Moreover, there are many patients who have received an implant system, e.g., a cochlear implant system of the type described in U.S. Pat. No. 5,603,726, incorporated herein by reference, which system includes both an implantable cochlear stimulator (ICS) attached to an electrode array that is inserted inside of the cochlea, and an external (non-implanted) battery, speech processor and headpiece. The speech processor (SP) and battery are housed within a wearable unit that is worn or carried by the patient, e.g., on a belt pack. The headpiece includes the external ac coil, a magnet, and a microphone. It is connected to the wearable unit via a cable. In use, the headpiece is positioned next to the external skin of the patient in close proximity to the ICS so as to provide efficient inductive coupling thereto. The magnet properly positions and holds the headpiece against the ICS implant location. Many of the patients who have and use the existing ICS system could greatly benefit from a fully implantable system, i.e., a system that eliminates the need for constantly wearing and/or carrying the external components of the system.
The present invention addresses the above and other needs.